Caffeine and Dehydration

Ask the Coach

Caffeine seems to help me get through a race but, with summer's heat, should I worry I'll get dehydrated? ...

Illustration by Jeremy Duncan

Caffeine seems to help me get through a race but, with summer's heat, should I worry I'll get dehydrated if I ingest too much?

—Terry Waddell, Tulsa, OK

Over the years we have been warned against caffeine because of dehydration. Now, all those scary caffeine stories are apparently like ghost stories around a campfire: More boo than true.

A study in a recent journal from the American College of Sports Medicine backs that up: Researchers in Spain tested trained cyclists during a hard, two-hour ride in nearly 100-degree, moderately dry heat, feeding them water or an electrolyte sports drink or nothing at all. They repeated the same trial with riders taking caffeine pills 45 minutes before exercising equal to 6 mg per kilogram of body weight (e.g. for a 165 pounder about 450 mg or the equivalent of three very strong cups of coffee).

The result? Caffeine increased urine output and electrolytes in the sweat, but neither was enough to make riders become less able to dissipate heat, get dehydrated or cause an electrolyte deficiency. Since several riders needed a break to relieve themselves, researchers from the Spain study concluded that the effects should be weighed against "the detriment in performance caused by time wasted to void."